Method of installing a heat tube on pre-insulated piping

ABSTRACT

A method is shown for installing a heat tube on a section of pre-insulated piping. A metal carrier pipe is covered with a first layer of foam insulation. Next, a routing device is used to cut a longitudinal slot along the length of the pipe so that the pipe exterior surface is exposed from the insulation. A heat tube is then installed within the longitudinal slot, whereby the heat tube contacts the exterior surface of the metal carrier pipe. A second layer of foam insulation is then sprayed onto the exterior of the metal carrier pipe, covering the previously formed longitudinal slot and installed heat tube. A polyolefin coating is then applied over the insulation to form a protective outer jacket for the insulated pipe.

1. CROSS REFERENCE TO RELATED APPLICATIONS

The present case is a continuation-in-part of an earlier filed application Ser. No. 16/017,377, filed Jun. 25, 2018, now U.S. Pat. No. 10,525,619, by Thomas Joseph Keyes, which, in turn, was a continuation-in-part of Ser. No. 15/583,506, filed May 1, 2017, now U.S. Pat. No. 10,421,232, by Thomas Joseph Keyes, both entitled “Method of Installing a Heat Tube on Pre-Insulated Piping”.

2. FIELD OF THE INVENTION

The present invention relates generally to fully bonded foam pre-insulated piping systems and, more specifically, to a method for installing a heat tube on such a pre-insulated pipeline.

3. DESCRIPTION OF THE PRIOR ART

Insulated pipelines are needed in a variety of situations. For example, distributed HVAC (heating, ventilation, and air conditioning) applications utilize chilled water for cooling and steam and hot water for heating. The chiller and boiler are typically contained in a central location and the chilled water and steam and hot water are distributed to other locations. For example, on a school campus the chiller and boiler may be located in a power plant building. The chilled water and steam are distributed to classrooms in separate buildings. A set of insulated pipelines is used to convey the chilled water from the chiller to other locations and back to the chiller. Another set of insulted pipelines is used to carry the steam or hot water from the boiler to the other locations and back to the boiler. It is necessary for the pipes to be insulated in order to retain the internal temperature of the medium being transported and keep heating and cooling losses at a minimum. The insulated pipelines are usually located underground.

So called “pre-insulated piping systems” of the type under consideration are conventional and commercially available. There are predominately two types of such pre-insulated piping systems in use: Class-A drainable dryable testable (DDT); and polyurethane or polyisocyanurate “fully bonded” foam systems. In the bonded type system, the foam and outer jacket, being bonded, do not move relative to the inner pipe. In the Class-A type system, on the other hand, the insulated inner pipe is designed to move independently of the associated outer jacket. In fact, there is an air gap between the inner pipe and outer carrier pipe in the class-A type system.

The present application is directed toward the bonded foam type system. These systems utilize a metal carrier pipe, typically of steel, to convey fluid, i.e., steam and/or superheated water, where the fluid is at a different temperature as compared to the ambient environment. In the particular types of piping systems under consideration, the pipelines may also be used to convey process fluids, heating water and hydrocarbon products, for example. In any event, around the outside of the steel pipe is a layer of insulating foam such as, for example, a polyurethane foam or a polyisocyanurate foam. In the case of high temperature piping systems, the insulating foam serves to keep heat loss from the starting location of the pipeline to the ending location at a minimum. Around the outside of the foam is a thin jacket of thermoplastic material, such as high density polyethylene (HDPE). The plastic jacket protects the foam from mechanical damage and also provides a watertight seal to prevent corrosion of the steel pipe.

In the typical pre-insulated piping manufacturing process, the steel carrier pipe is typically rotated while a foam dispensing head passes down the length of the pipe applying the foam coating. Alternatively, a helical conveyor system may be used to rotate the pipe as it travels down the conveyor. In other known processes, an outer envelope is placed about the length of the inner carrier pipe and foam is then injected from one end into the annular area between the pipe exterior and the interior of the outer envelope.

The above type processes have been used for many years and are adequate for most types of pre-insulated piping systems. However, in some cases, it is desirable to install what is called a “heat tube” on the exterior of the inner steel carrier pipe. Heat tubes are used, for example, as a part of “heat tracing” systems. Heat tracing is the use of an externally applied heat source on a pipeline to compensate for heat losses through the thermal insulation. Heat tracing evolved because of the need to maintain the flow of low, medium and high temperature liquids through a pipeline, whatever the nature of the surrounding environment. These type systems are commonly used for temperature maintenance and freeze protection and in heating/reheating applications in the transport of process fluids, heating water and heavy petroleum products. The term “heat tube”, as used in the discussion which follows, is also intended to cover other applications, such as where the tubes carry electrical wires or cables for other purposes than heat transfer. For purposes of explaining the method of the invention, however, an electric heat tracing system will be utilized.

Various types of heat tracing systems exist. However, electric heat tracing systems offer significant advantages. Generally speaking, electric beat tracing supplies only the heat necessary for the efficient flow of product through the pipeline, and only when required. Because electric tracing is easily controllable, temperature variance is minimized and operating costs are significantly reduced. Time consuming costly purging of the heat lines is also eliminated in many cases.

Whatever type of electric heat tracing system is, it is generally necessary to install the previously described “heat tube” on the exterior surface of the metal carrier pipe. The heat tube is typically a metal or plastic conduit or channel member which is used to contain the electrical cabling or wiring used in the system and to transfer heat to the inner metal carrier pipe, as will be described more fully in the description which follows. The installation of the heat tube on the exterior surface of the inner metal carrier pipe presents some challenges in the case of pre-insulated piping systems, however, due to the presence of the outer foam insulating layer and the outer protective jacket.

Thus, there continues to be a need for improvements in the pre-insulated piping manufacturing processes, particularly where a heat tube is to be installed for such purposes as an electric heat tracing system.

It is, therefore, an object of the present invention to provide a simple and cost effective process for installing such a heat tube on the exterior surface of the inner metal carrier pipe as a part of a pre-insulated piping system.

SUMMARY OF THE INVENTION

The present invention concerns a method for installing a heat tube on a section of pre-insulated piping. The pre-insulated piping is made up of first and second lengths of insulated and jacketed pipe, each having a joining end to be joined to an end of the other length. Each pipe length comprises an inner metal carrier pipe having an interior surface and an exterior surface, an envelope of foamed insulation surrounding the inner metal carrier pipe exterior surface, and an outer protective jacket surrounding the envelope of insulation. The joining ends of adjacent metal carrier pipe lengths are welded together to form fixed joints, whereby the adjacent pipe lengths provide a continuous length of fluid conduit for conveying fluids.

The preferred method of the invention comprises the steps of:

providing a steel carrier pipe having an exterior surface, an interior surface and a given length extending along a central longitudinal axis, the steel carrier pipe having a first layer of foam which has previously been sprayed onto the exterior surface thereof, the foam covered pipe having also been cured at a curing station to allow the sprayed foam to cure to a given radial thickness to thereby form a foam insulated pipe; placing the foam insulated pipe on a conveyor and moving the foam insulated pipe down the conveyor to a cutting station which includes a cutter assembly; providing a carriage assembly located at the cutting station which is associated with the cutter assembly and moving the carriage assembly on as associated track linearly down the exterior of the foam insulated pipe, whereby the cutter assembly cuts a longitudinal slot through the first layer of foam insulation along at least a portion of the length of the steel carrier pipe, thereby exposing the exterior surface of the steel carrier pipe; installing a heat tube within the longitudinal slot whereby the heat tube contacts the exposed exterior surface of the metal carrier pipe; passing the pipe past a second foam application station while spraying a second layer of foam insulation onto the exterior of the metal carrier pipe, thereby covering the previously formed longitudinal slot and installed heat tube; applying a synthetic polymeric coating around the insulated pipe to thereby form an outer protective jacket for the insulated pipe.

The cutter assembly can assume various forms, but can conveniently comprise a wire brush or a blade, or other device capable of cutting or forming a longitudinal channel in the first layer of foam insulation which is applied onto the exterior surface of the metal carrier pipe.

The lengths of insulated piping being joined can be used, for example, as a part of a pipeline conveying process fluids, heating water or petroleum products. The insulated pipes can be used as a part of an electric current tracing system which is used for temperature maintenance and freeze protection.

The preferred insulating foams are selected from the group consisting of polyurethane foams and polyisocyanurate foams. The carrier pipe being insulated is a metal pipe which is preferably formed of steel of a given gauge. One preferred material for the outer protective jacket is a high density polyethylene jacket material.

The process for installing a heat tube on the exterior surface of the inner metal carrier pipe can be performed in a batch manufacturing operation, or in a continuous or semi-continuous operation, as will be described more fully in the written description which follows.

Additional objects, features and advantages will be apparent in the written description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified representation of a typical prior art pro-insulated electric heat traced steel piping installation.

FIG. 2 is a simplified, schematic view of the first step in the manufacturing process of the invention in which an inner metal carrier pipe is coated with a layer of foam insulation.

FIG. 3 is a simplified view, similar to FIG. 2, showing the next step in the process in which a wire electric brush is used to cut a longitudinal slot in the previously applied layer of foam insulation.

FIG. 3A is a simplified, isolated view of a blade fixture which can also be used as the routing device in the process of the invention.

FIG. 4 is a view of the next step in the process of the invention in which a steel heat tube is installed in the previously cut slot.

FIG. 5 is illustrates the next step in the process in which an additional layer of foam insulation is applied to the partly insulated pipe, covering the steel heat tube and longitudinal slot.

FIG. 6 is illustrates the final step in the process of the invention in which an outer protective synthetic jacket is applied about the exterior of the previously insulated pipe and steel heat tube.

FIGS. 7A and 7B are simplified, partly schematic views of a continuous manufacturing process for installing a heat tube on pre-insulated piping in which a cutting device is mounted in a suitable fixture and the foam insulated carrier pipe is moved past the fixture in linear fashion to form a longitudinal slot in the first layer of foam on the foam insulated carrier pipe.

FIGS. 8A to 8C are simplified, partly schematic views of another version of a continuous manufacturing process in which the cutter assembly is moved down a stationary foam insulated pipe to cut a longitudinal slot in the foam.

FIG. 9 is an isolated view of the carriage assembly which is used to pull the cutter assembly down a longitudinal track using rack and pinion gear assemblies.

FIG. 10A is an isolated view of one of the side cutting blades used in the cutter assembly of the invention.

FIG. 10B is a perspective view of the cutting blade of FIG. 10A.

FIG. 10C is an isolated, perspective view of the entire cutter assembly.

FIG. 10D is a front end view of the cutter assembly of FIG. 10C.

FIG. 10E is a side view of the cutter assembly of FIG. 10C.

DETAILED DESCRIPTION OF THE INVENTION

The preferred version of the invention presented in the following written description and the various features and advantageous details thereof are explained more fully with reference to the non-limiting examples included in the accompanying drawings and as detailed in the description which follows. Descriptions of well-known components and processes and manufacturing techniques are omitted so as to not unnecessarily obscure the principle features of the invention as described herein. The examples used in the description which follows are intended merely to facilitate an understanding of ways in which the invention may be practiced and to further enable those skilled in the art to practice the invention. Accordingly, the examples should not be construed as limiting the scope of the claimed invention.

As has been briefly described, the particular type of piping system under consideration includes lengths of insulated and jacketed pre-insulated piping and, more specifically to a bonded foam pre-insulated piping system; i.e., the piping is made up of an inner carrier pipe having an interior surface and an exterior surface with an envelope of foamed insulation surrounding the inner pipe exterior surface. The envelope of foamed insulation can be, for example, an insulating material selected from the group consisting of polyurethane foams and high temperature polyisocyanurate foams. An outer protective jacket surrounds the envelope of insulation. The outer jacket can conveniently be formed from a polyolefin, such as a high density polyethylene. Each length of piping has a joining end for joining to an adjacent length of piping, whereby the adjacent lengths of piping provide a continuous length of fluid conduit for conveying high temperature fluids. The section of piping, as previously described, is installed in a piping system made up of other sections of piping.

One example of a commercially available pre-insulated piping system of the above type is the “HT-406” ™ High Temp Steel Piping System sold by Thermacor Process, Inc., 1670 Hicks Field Road East, Fort Worth, Tex. 76179. The following references, among others, teach the manufacture of such prior art systems: U.S. Pat. Nos. 3,793,411; 4,084,842; and 4,221,405, all to Stonitsch et al.; as well as U.S. Pat. Nos. 6,547,908; 5,736,715; 7,037,557; 7,418,979; and 9,377,150, all assigned to Thermacor Process, Inc., the assignee of the present invention.

Any reference in this discussion to “sections” or “lengths” of pipe is intended to refer to standard available factory pre-insulated piping of the type previously described having an inner metal pipe surrounded by an envelope of foamed insulation, which in turn, is contained within a polyolefin jacket. As referred to briefly above, typical commercial practice involves the use of steel, copper, aluminum or alloy metal material for the inner carrier pipes. The typical pipe diameters will be, for example, 4 inches to 12 inches. The insulating foam may be, for example, a suitable polyurethane foam. For high temperature systems, the surrounding envelope of foam insulation is typically formed of closed cell polyisocyanurate. The outer protective jacket in such systems can be formed of a suitable polyolefin, such as polypropylene, polybutylene, polyethylene, polyvinylchloride and similar protective jackets.

The term “high temperature”, as used in this discussion, means that the pipelines are conveying fluids at temperatures above ambient, typically at temperatures of 212° F. and above. In some cases, temperatures of 350°−400° F. and higher will be encountered. The expected operating temperature of the pipeline will determine the type of outer foam insulation utilized. For example, 250° F. is generally accepted as the present temperature limitation at which polyurethane foam is used in bonded foam systems. Temperatures above about 250° F. generally require the use of higher temperature foams, such as the previously mentioned polyisocyanurate foam. For example, a typical steam line might be conveying fluid at, for example, 250-350° F. In the case of the “heat tracing” systems of the type to be described, the piping system may be used, for example, as a part of a pipeline conveying process fluids, heating water or petroleum products. In such cases, the fluid being conveyed may be at a lower temperature, so that a polyurethane foam insulation is sufficient.

Several types of electric heat tracing methods are available, depending upon the end application. For example, one type is known as “skin effect tracing.” Electric skin effect current tracing can be thought of as combining the engineering principles of “skin effect” and “proximity effect.”

Skin effect is an alternating current phenomena whereby AC current flows in the outer surface of a steel conductor. Proximity effect is an electromagnetic force which operates based upon the fact that equal currents in opposite directions attract. By placing the electric cable inside the heat tube, the current is drawn to a thin section of the heat tube inner wall. Heat generated from the current passes through the heat tube wall and into the steel carrier pipe by conduction. Exterior surfaces of skin effect current systems are electrically grounded. The voltage is impressed between the cable and the inner surface of the heat tube.

Skin effect heating allows a single point connection to provide heat for distances as long as 15 miles and even greater. Since electricity only flows on the inside of the heat tube, any residual voltage is eliminated. Since skin effect heating allows the heat applied to be evenly dissipated over long distances, an even temperature profile can be achieved.

One skin effect heating system is sold by Thermacor Process, Inc., Fort Worth, Tex., as the Ferro-Therm HDPE Skin Effect Heating System™. Exemplary Specifications, somewhat simplified for ease of explanation, include the following:

A. Carrier Pipe shall be steel ASTM A-53, Grade B, ERW (Type e) or seamless (Type S), standard weight Piping shall generally be provided in 40 foot double random lengths where feasible. Straight sections of factory insulated piping shall have 6″ of exposed pipe at each end for field joint fabrication. B. A steel heat tube (cylindrical conduit) of A106, Seamless Sch. 40 pipe will be installed along the entire length of the carrier pipe. This could also be a channel member to accomplish the same purpose. C. An electric skin effect heat trace system will be custom designed for the specific application and installation conditions. D. Polyurethane foam insulation shall be used to cover the carrier pipe in the annular space between the carrier pipe and the ultimate outer HDPE jacket with a minimum thickness of one inch. Insulation shall be rigid 90-95% closed cell polyurethane with a 2.0-3.0 pounds per cubic foot density and coefficient of thermal conductivity 9K-factor) of 0.14 and shall conform to ASTM C-591. E. The outer jacketing material shall be extruded black, high density polyethylene (HDPE) manufactured in accordance with ASTM D-1248 having a minimum wall thickness of 150 mils.

The above specification extracts are intended to be exemplary only as the specifications may vary to some extent, depending upon the end application for the heat trace system. These specifications are intended to provide some understanding of the basic types of materials used in a typical system of the type under consideration.

Turning now to FIG. 1, there is shown in somewhat simplified fashion a heat tracing system, which in this case happens to be an “electric skin effect heat trace system.” There are typically six main components in most skin effect systems. A control panel 11 is used to monitor the process temperature and to adjust the power input. A transformer 13 is used to regulate the voltage applied to the system. Various temperature sensors 15 are used to monitor the process temperatures. Skin effect electrical wires or cabling 17 are used to carry the voltage over the length of the pipeline system. Tubing or channeling 19 provides protection for the electrical wires and dissipates the heat energy to the pipeline. Junction boxes, such as pull box 21 and end termination box 23 are used for wire connection and wire pulling points.

This somewhat schematic illustration of a typical skin effect heat tracing system is intended to be exemplary only of one type of heat traced piping system. However, for whatever type heat traced system happens to be under consideration, there is generally the need to provide a “heat tube” to house the various electrical wires or cabling used in the system. FIGS. 2-6 which follow illustrate the improved method of the invention which is used to install such a heat tube on a section of pre-insulated piping.

Turning to FIG. 2, there is shown, in simplified fashion, the first step in one version of the manufacturing process of the invention. The method is used for installing a heat tube on a section of pre-insulated piping where the piping is made up of first and second lengths of insulated and jacketed pipe, each having a joining end to be joined to an end of the other length. Each pipe length comprises an inner metal carrier pipe having an interior surface and an exterior surface. An envelope of foamed insulation surrounds the inner metal carrier pipe exterior surface, and an outer protective jacket surrounds the envelope of insulation. The joining ends of adjacent metal carrier pipe lengths are eventually welded together to form fixed joints, whereby the adjacent pipe lengths provide a continuous length of fluid conduit for conveying fluids, as has been described.

In the first step of the method illustrated in FIG. 2, a section of steel carrier pipe 25 has an exterior surface 27, an interior surface 29 and a given length (‘T’ in FIG. 3) extending along a central longitudinal axis 31. The carrier pipe is placed on a helical conveyor system which rotates the pipe as it translates down the conveyor. A fixed foam dispensing head 35 sprays a layer of insulating foam 38 on the carrier pipe as it passes through the spray head path. As has been discussed, this might be a polyurethane foam sprayed to a depth of, for example, one inch thick. This part of the process is conventional and will be familiar to those skilled in the relevant arts.

The first layer of insulating foam will generally be sprayed to a depth which corresponds approximately with the height of the heat tube to be installed later. The layer of foam insulation is allowed to cure to a given radial thickness to thereby form a foam insulated pipe. It may be necessary to utilize more than one dispensing head 35, for example, one head above the pipe and one head below the pipe for evenly injecting foaming material as the heads move down the length of the rotating pipe.

In the next step in the method, shown in FIG. 3, a routing device is used to cut a longitudinal channel or opening down a selected length of the foam covered pipe. For example, a wire brush 37 can be mounted in a suitable jig fixture 39 on the side of the foam insulated pipe 25. In one version of the method of the invention, the pipe 25 is drawn past the wire brush 37 in a linear direction of travel to thereby cut a longitudinal slot 41 through the first layer of foam insulation at one point on the circumference of the steel carrier pipe, thereby exposing the exterior surface 27 of the steel carrier pipe 25. The slot may be, for example, about one inch by one inch in dimension. The wire brush can be something as simple as a typical wire wheel brush mounted on an electric drill body. Suitable wire wheels and drill bodies are available at Home Depot®, Lowes® and similar stores.

The routing device could also assume other forms, for example, FIG. 3A shows a simple stationary blade 34 mounted in a suitable fixture 36. As the foam covered pipe passes longitudinally past the routing station, the blade cuts a longitudinal slot such as the slot 41 shown in FIG. 3.

FIG. 4 illustrates the next step in the method in which a metal or plastic heat tube 43 is installed within the longitudinal slot 41, whereby the heat tube 43 contacts the exposed exterior surface 27 of the metal carrier pipe 25. The heat tube 43 may be temporarily affixed to the pipe exterior surface in some manner, but it is typically not necessary to weld the heat tube in place. The heat tube 43 is shown as being a cylindrical conduit in the drawings, but it will be understood that the heat tube could have other shapes, such as a square or rectangular channel member, for example.

FIG. 5 illustrates the next step in the method in which a second layer of foam insulation 42 is sprayed onto the exterior of the metal carrier pipe and first layer of foam insulation 38, thereby covering the previously formed longitudinal slot 41 and installed heat tube 43.

In the final step in the process, shown in FIG. 6, an outer protective synthetic jacket 45 is applied to the carrier pipe and two layers of foam insulation. This can be accomplished, as by applying a polyolefin coating (HDPE) around the insulated pipe to thereby form an outer protective jacket for the insulated pipe. In the example illustrated in FIG. 6, an extruder head 47 extrudes the HDPE coating from an extrusion nozzle 49 as the extrusion head passes longitudinally along the exterior of the pipe. Alternatively, the extruder head can be stationary with the pipe being placed on a helical conveyor system which rotates the pipe as it translates down the conveyor.

The steps in the method which have previously been described could apply to a batch, stepwise process, or to a continuous or semi-continuous process. FIGS. 7A and 7B illustrate one embodiment of such a continuous process.

With reference to FIG. 7A, a steel pipe 51 rolls off onto a conveyor line 53 and moves from right to left, as viewed in the top portion of FIG. 7A. The pipe is being translated in a longitudinal direction and also simultaneously rotated as it travels down the conveyor line. After traveling down a given length of the conveyor line 53, the pipe passes a foam application station 55 where a dispensing head 57 sprays a first layer of insulating foam onto the steel pipe. The foam may be sprayed, for example, to a depth of about 1.5 inches to match the general height of the heat tube to be installed.

With reference to the top portion of FIG. 7B, the pipe then enters the curing oven section 59 of the conveyor line and continues to move to the left as viewed in the top portion of FIG. 78. At the far left end of the drawing, the pipe is rolled off onto the second, straight line section of a conveyor line 61. The now foam covered pipe 63 moves from left to right, as viewed in the mid-section of FIG. 7B and continues over to a routing station (shown as 65 in FIG. 7A). In this version of the method of the invention, the previously described wire brush or blade routing processes are then used to cut a longitudinal channel down the length of the foam covered pipe 63, as described with respect to FIGS. 3 and 3A.

The foam covered pipe 63, having the routed longitudinal channel or groove previously described, then rolls off the end section 67 of the straight line conveyor onto a work station (designated as 69 in FIG. 7A). The previously described length of heat tube is then installed, in this case by hand, into the longitudinal channel cut in each length of pipe 71.

The lengths of pipe 71 then pass to another conveyor section 77 which both translates the lengths of pipe longitudinally and also simultaneously rotates the lengths of pipe. The lengths of pipe 71, having the installed heat tubes, are then moved from right to left, as viewed in the bottom portion of FIG. 7A, where they pass a second foam application station 73 where a dispending head 75 sprays a second layer of foam to cover the heat tube and open channel. The thickness of the second application of foam is determined by the required process specification thickness.

The lengths of pipe 71 then pass through an application station (79 in FIG. 7B) where they are sprayed by dispensers 81, 83, with a vapor barrier and wrapped with the polyethylene outer jacket previously described. The finished pipe lengths 85 then pass from right to left, as viewed in the bottom portion of FIG. 7B and roll off to a finishing area 87. The process line used in the continuous, or semi-continuous process described can easily run on the order of fifteen feet per minute.

FIGS. 8A to 10E illustrate another embodiment of the present invention in which the foam insulated pipe is stationary and a cutter assembly moves down the longitudinal axis of the carrier pipe in linear fashion to cut a longitudinal slot in the foam. Turning first to FIG. 8A, there is shown a supply 89 of previously manufactured foam insulated metal carrier pipes located adjacent a conveyor 91. The previously manufactured foam insulated pipe 89 could have been manufactured as previously described with reference to FIGS. 7A and 7B of the Drawings. In other words, these sections of pipe already have a first layer of foam insulation applied on their exterior surfaces but do not yet have a longitudinal channel. In FIG. 8A, one stand of pipe 93 has been fed onto the conveyor section 91.

With reference now to FIG. 8B, there is shown a top view of the next section of conveyor, designated generally as 95. This section of conveyor would receive the stand of pipe 93 from FIG. 8A and would move the pipe in linear fashion, from left to right as viewed in FIG. 8B and into position with one end of the pipe adjacent the cutter assembly 99. The stand of pipe 93 is not shown in FIG. 8B so that it does not obstruct the view of the conveyor section 95 and other operative parts of the assembly.

Once the section of pipe 93 abuts the leading edge 101 of the cutter assembly 99, any linear movement of the pipe section stops so that the pipe section is now held in stationary fashion. The cutter assembly 99 is now moved down the longitudinal axis of the stationary pipe section to cut one or more longitudinal slots in the foam which is located on the exterior surface of the carrier pipe. This is to be contrasted with the method of the invention shown in FIGS. 7A and 7B in which the pipe moved relative to the stationary routing station. The pipe section 93, with at least one longitudinal slot 103, is now fed linearly onto the conveyor section 105 and subsequently rolled off onto the storage area 107.

The above discussion describes the method used to cut a longitudinal slot in a previously insulated pipe. The pipe would then be further processed to apply the second layer of foam insulation and outer polyolefin jacket as has been described with respect to FIGS. 5 and 6.

FIGS. 9 to 10E show further details of the carriage assembly 97 and cutter assembly 99 used in the method of the invention. FIG. 9 is an isolated view of the carriage assembly 97 on its associated track with the cutter assembly removed for ease of illustration. The carriage assembly 97 can be provided with cam followers, such as rollers 109, 111, 113 shown in FIG. 9 which are mounted on associated rails, such as rails 115, 117 provided as a part of the track. Any of a number of suitable means can be utilized for moving the carriage assembly down the rails 115, 117 in linear fashion. For example, a simple rack and pinion mechanism (illustrated schematically as 119 in FIG. 8B) could be utilized. The cam followers eliminate tension and rotation of the carriage with respect to the associated track.

The carriage assembly is used to push and pull the cutter assembly 99 down the track formed by the associated rails 115, 117. In other words, the carriage assembly moves the cutter assembly down the exterior surface of the previously insulated metal carrier pipe to cut the longitudinal channel which will ultimately house the heat tube. The pipe is then moved further down the conveyor line and the carriage assembly and cutter assembly are retracted back to the original, starting positions in preparation for receiving a subsequent section of foam insulated pipe.

FIG. 10C is an isolated, perspective view of the cutter assembly 99. The cutter assembly has a generally arcuate body portion 121 which houses one or more cutter blade assemblies, such as the assemblies 123, 125, 127, shown in FIG. 10C. The assemblies 123, 125, 127 are generally equidistantly spaced about the arcuate body portion, extending outwardly along a longitudinal axis which is parallel to the longitudinal axis of the foam coated pipe. While the cutter assembly 99 shown in FIG. 10C uses three cutting blade assemblies, there could be other arrangements, such as the provision of only two, equidistantly spaced cutter blade assemblies. The top skin 129 of the cutter assembly 99 is designed to minimize blockage of the foam channel being formed.

Two identical runner assemblies 131, 133, connect to the carriage assembly 97 at two points by a cable (not shown) to maintain consistent pulling on the pipe exterior surface. The arcuate body of the cutter assembly 99 has lower side rails 135, 137 which house associated rollers, such as rollers 139 shown in FIG. 10C. The rollers allow the cutter assembly to ride on the conveyor and associated track shown in FIG. 9. The conveyor is not shown in FIG. 9, for ease of illustration of the carriage assembly and track, but can be seen as 95 in FIG. 8B. As shown in FIGS. 10D and 10B, each of the cutter blade assemblies, has hard plastic runners 141, 143, 145 which track on the pipe exterior surface during the cutting operation.

As can be seen in FIGS. 10A and 10B, each of the cutter blade assemblies has a hardened front cutting blade 147 which is preferably adjustable and replaceable and side cutting blades 149 which are also preferably adjustable and replaceable. There are also hard plastic runners, such as runner 151 located at the rear of each of the cutter blade assemblies which can be replaceable. The cutter blade assemblies can also be provided with compressed air ports (153 in FIG. 10B) for helping to clear the cut foam. They can also be provided with a recessed area 155 for receiving an optional abrasive brush which would be used to clean the metal exterior surface of the carrier pipe as the outer foam layer is being cut away.

In operation, a section of previously foam coated metal carrier pipe (93 in FIG. 8A) is moved down the conveyor sections 91 and 95 until the pipe leading end contacts the approximate location of the carriage and cutter assemblies (97, 99 in FIG. 8B) at a cutting station. The cutter assembly 99 is then pulled down the track from the right to the left, as shown in FIG. 8B. This action causes the cutter blade assemblies 123, 125, 127, to cut three longitudinal channels in the first layer of foam which coats the exterior of the metal carrier pipe. The section of pipe then moves further down the conveyor section 95 to last section of conveyor (105 in FIG. 8C) where it is then off-loaded to an adjacent area 107. In the meantime, the carriage and cutter assemblies 97, 99, are pulled from the left to the right, as viewed in FIG. 8B and returned to their original positions at the cutting station. A subsequent stand of foam insulated pipe is then moved down the conveyor section 95 to the approximate location of the carriage and cutter assemblies at the cutting station, as they are shown in FIG. 8B, and the process is repeated. The section of pipe with its longitudinal channels can then be processed as previously described with respect to FIGS. 5 and 6 to apply a second layer of foam insulation (FIG. 5) and then an outer protective layer of HDPE (FIG. 6).

An invention has been provided with several advantages. The method of the invention can be used to manufacture a length of pre-insulated piping where the lengths of insulated piping being joined are part of a pipeline conveying, for example, process fluids, heating water or petroleum products. The process accommodates the installation of one or more heat tubes of the type used in a heat tracing system used for temperature maintenance and freeze protection. The process is relatively simple in nature and economical to practice. The process can be easily integrated into existing pre-insulated foam pipe manufacturing processes.

While the invention has been shown in only one of its forms, it is not thus limited but is susceptible to various change and modifications without departing from the spirit thereof. 

What is claimed is:
 1. A method for installing a heat tube on a pre-insulated pipe, the method comprising the steps of: providing a pre-insulated pipe comprising: a steel carrier pipe having an exterior surface, an interior surface and a given length extending along a central longitudinal axis, and a first layer of cured foam insulation covering the exterior surface of the steel carrier pipe, the first layer of cured foam insulation having a given radial thickness; placing the pre-insulated pipe on a conveyor and moving the pre-insulated pipe down the conveyor to a cutting station which includes a cutter assembly connected to a carriage assembly and a linear track along which the carriage assembly can move; moving the carriage assembly along the linear track, whereby the cutter assembly is moved down the pre-insulated pipe and cuts a longitudinal slot through the first layer of cured foam insulation along at least a portion of the length of the steel carrier pipe, thereby exposing the exterior surface of the steel carrier pipe; installing a heat tube within the longitudinal slot whereby the heat tube contacts the exposed exterior surface of the steel carrier pipe; passing the pre-insulated pipe past a foam application station while spraying a second layer of foam insulation onto the exterior surface of the steel carrier pipe, thereby filling the longitudinal slot and covering the installed heat tube to form an insulated pipe; applying a polyolefin coating around the insulated pipe to thereby form a finished insulated pipe having an outer protective jacket.
 2. The method of claim 1, wherein the cutter assembly includes at least one blade.
 3. The method of claim 2, wherein the first layer of cured foam insulation and the second layer of foam insulation each comprise a material selected from the group consisting of polyurethane foam and polyisocyanurate foam.
 4. The method of claim 3, wherein the finished insulated pipe may be used as part of a pipeline for conveying process fluids, heating water or petroleum products.
 5. The method of claim 4, wherein the outer protective jacket is formed from a high density polyethylene jacket material.
 6. The method of claim 5, wherein the outer protective jacket is formed in the step of applying a polyolefin coating by spirally wrapping a polyolefin material about the insulated pipe.
 7. A method for installing a heat tube on a pre-insulated pipe, the method comprising the steps of: providing a steel carrier pipe having an exterior surface, an interior surface and a given length extending along a central longitudinal axis; placing the steel carrier pipe on a first section of a conveyor line which rotates the steel carrier pipe while simultaneously moving the steel carrier pipe in a longitudinal direction past a first foam application station where a first layer of foam insulation is sprayed onto the exterior surface of steel carrier pipe; passing the steel carrier pipe through a curing station located on a second section of the conveyor line located downstream of the first foam application station by moving the steel carrier pipe longitudinally down the second section of the conveyor line and allowing the first layer of foam insulation to cure to a given radial thickness to thereby form a pre-insulated pipe as it is being moved longitudinally down the second section of the conveyor line; passing the pre-insulated pipe to a third section of the conveyor line where it continues to be moved in a longitudinal direction to a cutting station which includes a cutter assembly connected to carriage assembly and a linear track along which the carriage assembly can move; moving the carriage assembly along the linear track, whereby the cutter assembly is moved down the pre-insulated pipe and cuts a longitudinal slot through the first layer of foam insulation along at least a portion of the length of the steel carrier pipe, thereby exposing the exterior surface of the steel carrier pipe; installing a heat tube within the longitudinal slot whereby the heat tube contacts the exposed exterior surface of the steel carrier pipe; after installing the heat tube, moving the pre-insulated pipe to a fourth section of the conveyor line which moves the pre-insulated pipe in a longitudinal direction while simultaneously rotating the pre-insulated pipe; passing the pre-insulated pipe past a second foam application station while spraying a second layer of foam insulation onto the exterior surface of the steel carrier pipe as the pre-insulated pipe is being rotated and moved in the longitudinal direction on the fourth section of the conveyor line, thereby filling the longitudinal slot and covering the installed heat tube to form an insulated pipe; moving the insulated pipe down a final section of the conveyor line while applying a polyolefin coating around the insulated pipe to thereby form a finished insulated pipe having an outer protective jacket; rolling the finished insulated pipe off the final section of the conveyor line into a finished pipe area.
 8. The method of claim 7, wherein the cutter assembly includes at least one cutting blade.
 9. The method of claim 8, wherein the first layer of foam insulation and the second layer of foam insulation each comprise a material selected from the group consisting of polyurethane foam and polyisocyanurate foam.
 10. The method of claim 9, wherein the finished insulated pipe may be used as part of a pipeline for conveying process fluids, heating water or petroleum products.
 11. The method of claim 10, wherein the outer protective jacket is formed from a high density polyethylene jacket material.
 12. The method of claim 11, wherein the outer protective jacket is formed in the step of applying a polyolefin coating by spirally wrapping the polyolefin coating about the insulated pipe.
 13. The method of claim 7, wherein the pre-insulated pipe is held stationary at the cutting station during the step of cutting the longitudinal slot.
 14. The method of claim 7, further comprising the steps of: moving the pre-insulated pipe further down the third section of the conveyor line after the longitudinal slot is formed; and retracting the carriage assembly back along the linear track to a starting position.
 15. The method of claim 7, wherein the cutter assembly comprises a generally arcuate body and one or more cutter blade assemblies housed in the generally arcuate body, the one or more cutter blade assemblies being generally equidistantly spaced about the generally arcuate body and extending outwardly along a longitudinal axis which is parallel to the central longitudinal axis of the steel carrier pipe.
 16. The method of claim 15, wherein each of the one or more cutter blade assemblies has a hardened front cutting blade which is adjustable and replaceable and a pair of side cutting blades which are also adjustable and replaceable.
 17. The method of claim 16, wherein each of the one or more cutter blade assemblies comprises a had plastic runner located at a respective rear of each of the one or more cutter blade assemblies. 